Perhaps the most striking feature of quantum mechanical
theory is the fact that it predicts that matter can behave like waves. This
means that coherent matter waves can form interference patterns, just like
the ones you would get if you combined two laser beams in an interferometer.
The demonstration of interfering pathways in a neutron interferometer was
perhaps the strongest affirmation of quantum theory and the wavelike nature
of matter. Atom interferometer experiments followed which extended this
demonstration to the size of an entire atom. But these experiments were
limited to showing that a single particle could interfere with itself. Now,
Bose-Einstein condensation has allowed us to make another advance, making
it possible to interfere two completely independent clouds of atoms with
each other.

Interference of two Bose condensates was demonstrated for the first time
in the month of November, 1996. This was done by cutting our atom trap
in half with an argon-ion laser beam. We then cooled the sodium atoms
in the two halves of the trap to form two independent Bose condensates.
At this point, we quickly turned off the laser and the magnetic fields,
allowing the atoms to fall and expand freely. As the two condensates began
to overlap with one another, interference fringes formed such as the fringes
in the images below.